SHE'S enjoyed the kind of stardust-scattered rise most politicians only dream of.

Four weeks ago, Jacinda Ardern was at home painting the fence in her trackpants, trying to work off the "nervous energy" of waiting for an election result.

On Thursday, the 37-year-old was crowned Prime Minister-elect following a month of negotiations to form a coalition government with the Greens and New Zealand First.

Jacinda Ardern spent the New Zealand election day painting the fence and having a BBQ. Picture: AFP PHOTO / MICHAEL BRADLEY.

Like Emmanuel Macron, 39, in France and Justin Trudeau, 45, in Canada, Ardern has ridden a wave of euphoria over her likability, relaxed style and fresh approach to politics.

She shut down radio hosts who asked about her baby plans, took selfies with school kids and even admitted she had been handed a "hospital pass" to the leadership. In seven weeks she reversed Labour's slide to gain 37 per cent of the national vote, leaving her competing with National's Bill English on 44 per cent, for the attentions of New Zealand First leader Winston Peters to form a coalition government.

The deal struck will offer Peters the role of Deputy Prime Minister and four cabinet posts. However it could also include major policy concessions and become an Achilles' heel given Peters' experience as a kingmaker and the party motto of "refusing to accept defeat in any cause we believe in".

Act Party leader David Seymour said it leaves a "weak Left coalition beholden to a madman on the loose."

The man who's party scored just 0.5 per cent of the vote said the "perverse marriage" that Labour and the Greens had created threatens millenials, immigrants and businesses.

"The silver lining for the centre-right is that the three-ringed circus is likely to fall apart - perhaps even before its three years are up," he said.

"The Greens and New Zealand First despise each other, and Winston Peters has caused chaos in every government he's joined. New Zealanders may face an election sooner than they think."

United Future MP Peter Dunne echoed that sentiment to Green Party leader James Shaw, saying he was now in charge of keeping an "unruly new partner" in line.

Prime Minister-elect Jacinda Ardern has signed a deal with Winston Peters, who at 72 is intent on preserving a political legacy. Picture: Hagen Hopkins/Getty Images.

The veteran politician and kingmaker in NZ politics will drive a hard bargain for his support. Picture: AFP PHOTO / Marty MELVILLE

Peters said he decided to pair with Labour and the Greens because they offered the best way

to mitigate what New Zealand is expected to face in the years ahead.

"It's time for capitalism to regain its human face," he said. "Our perception was the people of this country did want change and we've responded to that."

But the political marriage could prove an uneasy alliance for the parties that have starkly different platforms on immigration and business.

Peters wants a ban on foreign ownership of residential and farm land, net migration slashed to 10,000 per year and to create a low tax environment.

In contrast, Labour campaigned on New Zealand being a country "built on immigration" and wants to increase the refugee quota to 1500. It also wants to crack down on foreign property speculators and has planned to build 100,000 new homes across the country.

Whatsmore, at 72 Peters thinks it's "now or never" to leave a mark on New Zealand after nearly 40 years in politics.

"Frankly, of late, I've been asking myself that question because we're coming to an election and I kind of think it's now or never," he said in August.

"If we don't turn it around, and you've all got your different views, but if you were remotely neutral and you examined New Zealand - where it once was as a country in the Western world to where it is now ... you'd have to admit we've done very badly."

While supporters celebrate smashing a decade of right-wing rule, if Ardern wants to avoid the popularity slumps seen by Trudeau and Macron since they took office, her greatest political challenge yet may come from within.